1. Field of the Invention
Embodiments of the present invention relate to a recording apparatus, medium, and method controlling a write operation of the recording apparatus, and more particularly, to a disk drive, medium, and method of compensating for a write parameter in order to prevent a weak write and an over write by taking into consideration the Thermal Pole Tip Protrusion (TPTP) characteristics of a corresponding head.
2. Description of the Related Art
A hard disk drive is a device that can be used record and/or reproduce information. The information may be written in concentric tracks on a surface of at least one magnetic write disk mounted on a spindle motor, and may be accessed by a read/write head mounted on an actuator arm, rotatable by a voice coil motor. The voice coil motor is magnetized by a current and rotates the actuator arm, thereby moving the read/write head across the disk. The read/write head can then sense changes in the magnetic field on the disk surface, thereby reading information recorded to the disk. Current can be supplied to the read/write head in order to write information to data tracks of the disk. Here, the current causes a magnetic field to magnetize particular regions of the disk surface.
The greater the capacity of a hard disk drive, the smaller permitted margin of error. In particular, over writing can become a serious problem in high density and high capacity hard disk drives. Therefore, it becomes important to precisely control the write current in a corresponding write operation.
Even though the write current may be constant while writing data to the hard disk drive, the intensity of magnetic field actually varies during the write operation as the temperature of the read/write head increases, according to the progress of the write operation. As the temperature of the read/write head increases, according to the progress of the write operation, a pole tip protrusion of a write head changes, i.e., the influence of Thermal Pole Tip Protrusion (TPTP) changes. Consequentially, the gap between the read/write head and the disk, i.e., a flying height, changes.
As the result, at the beginning of a write operation data is written with less intensity then a preferred intensity, and as time passes, data is written with gradually larger intensities.
Conventionally, since the write current is only controlled based on an operational temperature, this does not efficiently deal with the write intensity variances as write operations progress.
FIG. 1 illustrates a hard disk drive system 10. Referring to FIG. 1, the hard disk drive system 10 includes a hard disk 20 that is installed on a base 11 in a rotatable manner, and a head transfer device that transfers a head (not shown) over a desired track on the hard disk 20 in order to read/write information. The hard disk 20 can be divided into a data area 22, where information can be written, and a parking area 21 where the head may be parked when the hard disk 20 stops rotating.
The head transfer device can include a head assembly 30 that includes the head and is pivotally installed on a pivot axis 34 disposed on the base 11, and a driver 40 that pivots the head assembly 30, using an electromagnetic force, for example.
The head assembly 30 may further include a suspension 31 along an end of an actuator arm 32, which is rotatably attached to the pivot axis 34, and a head slider 50 containing the head used to read/write information to/from the hard disk 20. The head slider 50 can be installed in the suspension 31.
The head slider 50 can be biased above the hard disk 20 by the suspension 31, floating over the hard disk 20 at a certain height due to dynamic air pressure generated by the rotation of the hard disk drive 20. The height (hereinafter referred to as “flying height”) of the head slider 50, floating over the hard disk 20, is based on opposing forces of the load, i.e., downward force (weight), of the suspension 31 and the lift force caused by airflow generated by the rotation of the hard disk 20.
Accordingly, the flying height denotes a gap between a read sensor, i.e., a magnetic resistance head at an end of the magnetic head slider 50, and a surface of the hard disk 20.
FIG. 2 illustrates a perspective view of a head. Referring to FIG. 2, a magnetic head 70 can include a magnetic resistance head 74 for reading from the hard disk 20, and an inductive write head for writing to the hard disk 20. The magnetic resistance head 74 senses magnetic fields of the hard disk 20. The inductive write head can include a top pole 71, a bottom pole 72, with the top pole 71 and bottom pole 72 being separated from each other by a fixed distance to form a leakage magnetic field for magnetizing a magnetic layer of the hard disk 20, and a write coil 73 to generate a magnetic field based on a supplied current, to apply a desired magnetic signal to the hard disk 20.
With the development of hard disk drives, corresponding Tracks per Inch (TPI) have increased and the width W of tracks has decreased, thereby increasing the capacity of the hard disk 20. In order to reduce the width W of track in the hard disk 20, the width of an inductive write head, to apply a magnetic signal to the tracks, should be reduced similar to the reduction in the width W of the track. Also, the flying height of the magnetic head 70 should be reduced to read the magnetic field of the written magnetic signal from the narrowed track. The flying height of the magnetic head 70 has a large influence on writing performance.
Conventionally, in order to cope with the change in coercive forces of a hard disk, due to changes in temperature, the write current can be modified, i.e., compensated, according to differences in room temperature. More specifically, the standard write current of a hard disk drive is set based on a room temperature when manufacturing the hard disk drive, and a write current is compensated according to the operating temperatures of the hard disk drive.
Although the write current can be adjusted based on the operating temperature of a hard disk drive, it is still a fact that a constant write current is still always supplied to a write head, despite of the progress of the write operation, i.e., there is no consideration taken for the length of operation. As described above, it is impossible to cope with a TPTP phenomenon where the amount of pole tip protrusion of the write head varies with the progression of the write operation.
A write magnetic head can be made up of a metal (usually, permalloy: Ni 80%/Fe 20%), and a slider to support the write magnetic head may be made up of a non-metal. Therefore, the write current flows through the metal coil, and then generates Joule heating during the write operation. However, the difference between the thermal coefficients of the metal and the non-metal causes the TPTP effect.
TPTP reduces the distance between the head and the disk (Head/Disk Interface: HDI), thereby lowering the flying height of the head. Therefore, write intensities, with respect to write currents with the same amplitude, actually differ according the degree of TPTP influence.
Accordingly, the degree of TPTP is proportional to i2R. Herein, i denotes the write current that flows through the write coil, and R denotes the resistance of the write coil. The resistance is a property of the write coil and is fixed when the head is manufactured. Here, i is determined by Write Current (WC) or Over Shoot Current (OSC) used for a drive. Since the degree of TPTP is proportional to a square of i, TPTP is more sensitive to i than to R.
FIG. 3 is a cross-sectional view of a head assembly 30. Referring to FIG. 3, the head assembly 30 can include a suspension 31, attached to an end of an actuator arm 32 toward a hard disk 20, and a magnetic head slider 50, installed on the end of the suspension 31 and biased to the suspension 31 by a gimbal 36 connecting the head slider 50 to the suspension 31.
As noted above, the flying height FH of the magnetic head slider 50 depends on the lift force caused by the airflow generated by the rotation of the hard disk 20 and the bias of the suspension 31. Accordingly, the suspension 31 can stably maintain the flying height FH of the magnetic head slider 50.
As illustrated in FIG. 3, the magnetic head 70 can be located at an end of the head slider 50.
FIGS. 4A and 4B illustrate cross-sectional views of the head assembly showing the influence of TPTP. FIG. 4A illustrates the state when reading is performed, and FIG. 4B illustrates the state when writing is performed. Referring to FIGS. 4A and 4B, a write pole tip shown in FIG. 4B protrudes farther than the write pole tip shown in FIG. 4A. This protrusion of the write pole tip results from a difference between thermal coefficients of the non-metal head slider 50 and the metal magnetic head 70.
With respect to data writing of the hard disk drive, the pole tip of the write head does not protrude much initially since the write head is not heated, but, as the duration of the write operation continues, the write head becomes heated, and the pole tip of the write head protrudes farther.
The write head is not sufficiently heated, initially, resulting in a weak write, and the write head overheats as a write operation continues, resulting in an over write and potential deletion of information in adjacent tracks.
Conventionally, since the write current is controlled based on the operating temperature of the hard disk drive, changes in the writing intensity as a write operation continues are not properly dealt with.